CN113845273B - Method for efficiently denitrifying and decarbonizing anaerobic effluent of pig wastewater - Google Patents

Abstract

The invention discloses a method for efficiently denitrifying and carbon-removing anaerobic effluent of pig raising wastewater. Firstly, polyacrylamide and polyaluminum chloride are used to remove suspended solids contained in incoming water in a coagulation and sedimentation system; In the future, the organic matter in the water will be transformed into organic acids again, as an effective carbon source for subsequent heterotrophic denitrification, while reducing COD, ensuring a suitable C/N ratio for subsequent nitrosation, anammox and denitrification reactions; using the SNAD system to remove Most of the ammonia nitrogen, total nitrogen and COD in the incoming water, by limiting the aeration of the reactor to ensure a certain concentration of free ammonia in the reactor to maintain the inhibitory effect on nitrite oxidizing bacteria, so that more ammonia nitrogen can be converted into nitrite and Finally, the anaerobic environment is maintained in the short-range sulfur autotrophic denitrification-ANAMMOX reactor to ensure that the ammonia nitrogen is not oxidized, and the sulfur dosage is controlled to reduce the sulfur dosage and save chemicals. purpose of consumption.

Description

A method for efficient denitrification and carbon removal of swine wastewater anaerobic effluent

technical field

The invention relates to the technical field of livestock and poultry breeding wastewater treatment, in particular to a method for efficient denitrification and carbon removal of pig raising wastewater through anaerobic effluent.

Background technique

The scale of my country's pig breeding industry is increasing day by day, and the discharge of pig farming wastewater is increasing. The statistics of the Second National Survey of Pollution Sources (June 8, 2020) pointed out that in 2017, the discharge of water pollutants from large-scale livestock and poultry farms nationwide included 6.0483 million tons of chemical oxygen demand (COD) and 75,000 tons of ammonia nitrogen. The total nitrogen is 370,000 tons. Pig farming wastewater is mainly composed of animal feces, urine, feed residues, and house flushing water. It mainly contains pollutants such as ammonia nitrogen and COD, which can lead to environmental problems such as eutrophication of water bodies and land pollution, and cause harm to people and the surrounding environment. Therefore, the denitrification technology for sewage and wastewater is extremely important.

At present, pig raising wastewater treatment plants are generally far away from urban areas, and the effluent is difficult to connect to municipal sewage pipelines. This requires that the treated sewage should have high water quality; however, the traditional nitrification and denitrification process has the problems of long residence time and high operating costs. . As environmental governance becomes more and more stringent, how to improve the sewage treatment process has become an urgent problem to be solved.

Contents of the invention

Aiming at the above-mentioned problems in the prior art, the present invention provides a method for efficient denitrification and carbon removal of pig wastewater anaerobic effluent. Nitrogen is treated with high efficiency and low consumption.

In order to achieve the above purpose, this application proposes a method for efficient denitrification and carbon removal of pig wastewater anaerobic effluent, including coagulation and sedimentation steps, anaerobic hydrolysis steps, synchronous nitrosation-anammox-denitrification steps, short-range sulfur Autotrophic denitrification-ANAMMOX step;

The coagulation and precipitation step is: adding 1-5 mg/L polyaluminum chloride (PAC), stirring at a speed of 50-200 r/min for 20-30 min, and then adding 0.8-1.2 mg/L polyacrylamide (PAM), stirring at a speed of 90-110r/min for 20-30min;

The anaerobic hydrolysis step is as follows: set the concentration of the inoculated sludge to 5000-12000 mg/L, the abundance of functional flora is higher than 20%, and the dissolved oxygen (DO) is controlled below 0.1 mg/L;

The step of synchronous nitrification-anammox-denitrification (SNAD) is: setting the inoculation sludge to contain anammox bacteria (Anammox), ammonia oxidizing bacteria (AOB), and heterotrophic denitrification bacteria to control anammox The abundance of oxidized species is not less than 3%, the filling ratio of the carrier filler is 25% to 40%, the specific surface area of the filler is 550 to 900m ² /m ³ , and the concentration of volatile suspended solids (MLVSS) in the mixed solution is 3000 to 5000mg/L. DO is controlled at 0.1-0.5mg/L, the temperature is 30-37°C, and free ammonia is controlled below 20mg/L;

The short-range sulfur autotrophic denitrification-anaerobic ammonium oxidation (SSuDA) step is: setting the inoculated sludge to contain Anammox bacteria and sulfur autotrophic denitrifying bacteria, using sulfur as the sulfur source, and the ratio of sulfur to sodium carbonate is 0.4 to 0.6 : 1. According to the synchronous nitrosation-anammox-denitrification step, the effluent ammonia nitrogen is 50-100mg/L, the nitrate nitrogen is 150-250mg/L, and the sulfur dosing concentration is determined to be 200-500g/L. The filled carrier The filling ratio is 20%~30%, the specific surface area of the filler is 650~750m ² /m ³ , the MLVSS of the mixed solution is 3000~5000mg/L, the temperature is 33~40℃, DO is controlled below 0.1mg/L; the final effluent quality NH ₄ ⁺ -N is controlled within 5 mg/L, total nitrogen concentration TN is controlled within 10 mg/L, and COD concentration is controlled within 150-300 mg/L.

Further, the total residence time of the above four steps is 51-136 hours, the residence time of coagulation and sedimentation reaction is controlled at 3-4 hours, the residence time of anaerobic hydrolysis reaction is controlled at 12-48 hours, and the synchronous nitrosation-anammox-denitrification The reaction residence time is controlled at 24-48 hours, and the residence time of the short-course sulfur autotrophic denitrification-anammox reaction is controlled at 12-36 hours. The above-mentioned times can be adjusted according to specific application conditions.

Further, the coagulation-sedimentation step is implemented in a coagulation-sedimentation system, and the coagulation-sedimentation system includes a coagulation stirring tank, a dosing tank a, a dosing tank b and a sedimentation tank a, and the dosing tank Polyacrylamide (PAM) is contained in a, and polyaluminum chloride (PAC) is contained in the dosing pool b, and the PAM and PAC enter the coagulation and stirring through the dosing pump a and the dosing pump b respectively. In the pool, the effluent from the coagulation mixing tank enters the sedimentation tank a for mud-water separation, and the sludge in the mud hopper is cleaned every day.

Further, the anaerobic hydrolysis step is implemented in an anaerobic hydrolysis system, and the anaerobic hydrolysis system includes an inlet pump and an anaerobic hydrolysis reaction tank, and the effluent of the sedimentation tank a is sent into the anaerobic hydrolysis reaction tank through the inlet pump Among them, an air outlet and a sampling port are provided on the top of the anaerobic hydrolysis reaction tank, which is convenient for monitoring and adjustment.

Further, the anaerobic hydrolysis reaction tank ensures a safe height between the mud layer and the water outlet by controlling the stirring speed, and a three-phase separator is installed at the water outlet to ensure the clarification of the water outlet.

Further, the synchronous nitrosation-ANAMMOX-denitrification step is implemented in a synchronous system, and the synchronous system includes a SNAD reaction tank, a flow meter, an aeration pump, a sedimentation tank b and a sludge return pump a , the effluent of the anaerobic hydrolysis reaction tank enters the SNAD reaction tank, the effluent of the SNAD reaction tank enters the sedimentation tank b for mud-water separation, the sludge enters the mud hopper and returns to the SNAD reaction tank through the sludge return pump a, and the SNAD reaction tank The part is connected to the aeration pump through a flow meter.

Furthermore, the air pumped in by the aeration pump is regulated by the flow meter to maintain the dissolved oxygen concentration in the SNAD reaction tank, so that the internal microorganisms are in a slightly aerated environment, ensuring that most of the total nitrogen Removal; the remaining part of ammonia nitrogen is used to maintain the concentration of free ammonia FA in the SNAD reaction tank, so as to inhibit the nitrite oxidizing bacteria NOB without interfering with the main strains, and ensure the degradation efficiency of total nitrogen and the stability of the strains in the reactor.

Further, the short-range sulfur autotrophic denitrification-ANAMMOX step is implemented in a short-range system, and the short-range system includes a reactor, a sedimentation tank c, a sludge return pump b, a dosing tank c, and a sedimentation tank c. The effluent from pool b enters the reactor, and the effluent from the reactor enters the sedimentation tank c for mud-water separation, and the sludge enters the mud hopper and returns to the reactor through the sludge return pump b; the sulfur and The sodium carbonate mixture adjusts the dosing amount through the dosing pump c to control the reduction of nitrate nitrogen to nitrite nitrogen instead of all reduction to nitrogen, and then performs anaerobic ammonia oxidation reaction with the ammonia nitrogen in the effluent of the sedimentation tank b to achieve The purpose of deep denitrification and reducing chemical consumption.

Furthermore, there are exhaust ports and sampling ports on the top of the SNAD reaction pool and the reactor;

As a further step, both the sedimentation tank b and the sedimentation tank c are equipped with a mud scraper, which operates intermittently for 5 minutes every 6 hours to ensure that the effluent is still clarified while removing the sludge on the wall of the sedimentation tank ; The bottom slope of the sedimentation tank b and c is set at 50°-70° to ensure that as much sludge as possible slides into the mud hopper and flows back into the SNAD reaction tank and reactor.

As a further step, the mixed solution of sulfur and sodium carbonate mixed with water after adding water in the dosing tank c has a water content of 10% to 15%; it is adjusted according to the concentration of nitrate nitrogen and ammonia nitrogen contained in the effluent of the SNAD reaction tank, Under the conditions of ensuring that all nitrate nitrogen is reduced to nitrite nitrogen and all ammonia nitrogen participates in the anammox reaction, the nitrite nitrogen that does not participate in the anammox reaction is reduced to nitrogen by the remaining sulfur, ensuring that the overall Efficient degradation of total nitrogen.

The above technical scheme that the present invention adopts, compared with prior art, has the advantage that:

(1) The present invention removes high-concentration ammonia nitrogen and COD contained in swine wastewater through coagulation sedimentation, anaerobic hydrolysis, SNAD process and SSuDA process, and each system has simple structure, high degree of automation and strong operability.

(2) The present invention controls the amount of aeration in the SNAD reactor to ensure that there is a certain concentration of free ammonia (FA) in the system, which effectively inhibits the activity of nitrite nitrogen oxidizing bacteria in the system and converts more ammonia nitrogen into nitrous The state nitrogen is finally converted into nitrogen by anammox bacteria and removed, thereby greatly improving the removal efficiency of the system for total nitrogen and saving aeration energy consumption.

(3) The present invention combines short-range sulfur autotrophic denitrification with anaerobic ammonium oxidation process, first maintains the anaerobic environment in the system to ensure that ammonia nitrogen is not oxidized, and controls the dosage of sulfur to ensure that all nitrate nitrogen is reduced to inferior Nitrate nitrogen and anaerobic ammonium oxidation with ammonia nitrogen in the reactor. Because the anaerobic ammonium oxidation process itself can generate alkalinity, compared with the whole sulfur autotrophic denitrification process, this process can achieve the purpose of reducing sulfur dosage and saving alkalinity consumption.

Description of drawings

Fig. 1 is a system structure diagram of anaerobic effluent efficient denitrification and carbon removal of pig raising wastewater;

In the figure: 1 coagulation mixing tank; 2 dosing tank a; 3 dosing pump a; 4 dosing pump b; 5 dosing tank b; 6 sedimentation tank a; 7 inlet pump; 8 anaerobic hydrolysis reaction tank; 10 flow meter; 11 aeration pump; 12 sedimentation tank b; 113 sludge return pump a; 14 reactor; 15 sedimentation tank c; 16 sludge return pump b; 17 dosing tank c; 18 dosing pump c.

Detailed ways

The embodiments of the present invention are implemented on the premise of the technical solutions of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

Example 1

A method for highly efficient denitrification and carbon removal of pig raising wastewater anaerobic effluent provided by the present invention is implemented in a pig raising wastewater treatment device. The pig raising wastewater treatment device includes a coagulation sedimentation system, an anaerobic hydrolysis system, a synchronization system and short-range systems;

The coagulation and sedimentation system includes a coagulation stirring tank, a dosing tank, a dosing pump, and a sedimentation tank; PAM (polyacrylamide) and PAC (polyaluminum chloride) in the water inlet and dosing tank are in the coagulation and stirring tank After being fully mixed, it is left to stand in the sedimentation tank, and the water outlet is connected to the anaerobic hydrolysis system, and the sedimentation tank is regularly discharged.

The anaerobic hydrolysis system includes a water inlet pump and an anaerobic hydrolysis reaction tank; the bottom of the anaerobic hydrolysis reaction tank is provided with a sewage water inlet, the top is provided with an air outlet and a sampling port, and a three-phase separator is installed at the water outlet; The reaction in the anaerobic hydrolysis reaction tank consumes organic nitrogen and part of COD; the outlet of the anaerobic hydrolysis reaction tank is connected to the water inlet of the lower part of the SNAD reaction tank of the synchronization system through a pipeline;

The synchronous system includes a SNAD reaction tank, a flow meter, an aeration pump, a sedimentation tank, and a sludge return pump; the lower part of the SNAD reaction tank is provided with a water inlet and an aeration system, and the upper part is provided with a water outlet, and the water inlet and the sludge return flow The pump is connected to the outlet of the anaerobic hydrolysis reaction tank; the SNAD reaction tank is loaded with fillers and activated sludge; the aeration system includes a flow meter, an aeration pump, and an aeration head, and the aeration head is connected to the aeration pump through a flow meter , to provide oxygen for the activated sludge in the SNAD reaction tank; the water outlet is connected to the sedimentation tank through a pipeline, and the sludge discharge port of the sedimentation tank is connected to the water inlet of the SNAD reactor through a sludge return pump.

The short-range system includes a reactor, a sedimentation tank, a sludge return pump, a dosing tank, and a dosing pump; the reactor water inlet is connected with the sedimentation tank of the synchronous system and the sludge return pump of the self-system, and is loaded with fillers and active Sludge, sulfur as a sulfur source and sodium carbonate providing alkalinity are pumped into the reactor through a dosing pump in the dosing tank, and the effluent can be directly discharged;

The filling amount of the biological filler in the SNAD reaction tank and the reactor is 20%-40% of their total volume. The main component of the biological filler is plastic, the model is K1, and the anaerobic ammonia oxidation biofilm grows on its surface.

The activated sludge filled in the SNAD reaction tank is nitrosifying bacteria, heterotrophic denitrifying bacteria and anammox bacteria. The activated sludge filled in the reactor is sulfur autotrophic denitrification bacteria and anaerobic ammonia oxidation bacteria. The anaerobic hydrolysis reaction tank 6 contains anaerobic hydrolysis bacteria.

A method for efficient denitrification and carbon removal of anaerobic effluent from pig raising wastewater. The specific implementation steps are: after coagulation and sedimentation, the incoming water is hydrolyzed and acidified in an anaerobic hydrolysis reaction tank, and most of the organic nitrogen and carbon are removed. COD; then remove about 80% of the total nitrogen in the SNAD reaction tank through the SNAD process, and maintain a certain concentration of ammonia nitrogen to ensure that there is 5-20 mg/L of FA (free ammonia) in the SNAD reaction tank to inhibit the activity of nitrifying bacteria , so that less nitrogen is converted into nitrate nitrogen; finally, in the reactor of the short-range system, the characteristics of sulfur autotrophic denitrifying bacteria preferentially reacting with nitrate nitrogen are used to control the dosage of sulfur to convert all nitrate nitrogen It is nitrite nitrogen, and then performs anaerobic ammonium oxidation with the ammonia nitrogen contained in the effluent of the SNAD reaction tank to complete the treatment process of total nitrogen.

Adopt method of the present invention to process pig raising waste water, concrete implementation case is as follows:

The water quality of the sewage generated after daily cleaning of pig houses in a pig farm after storage for 1-2 months: NH ₄ ⁺ -N 700-800 mg/L, COD 1200 mg/L. Applying the process described in the present invention, adopting the coupling process of synchronous nitrosation-anaerobic ammonium oxidation (SNAD) and short-range sulfur autotrophic denitrification-anaerobic ammonium oxidation, the hydraulic retention time is 48h, and the effluent NH ₄ ⁺ -N is lower than 10mg/L , NO ₂ - ^- N is lower than 1mg/L, NO ₃ - ^- N is lower than 1mg/L, the average removal rate of NH ₄ ⁺ -N and TN can reach 99%, and the average removal rate of COD is 80.1%.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling others skilled in the art to make and use various exemplary embodiments of the invention, as well as various Choose and change. It is intended that the scope of the invention be defined by the claims and their equivalents.

Claims (10)

1. The method for efficiently denitrifying and decarbonizing the anaerobic effluent of the swine wastewater is characterized by comprising a coagulating sedimentation step, an anaerobic hydrolysis step, a synchronous nitrosation-anaerobic ammoxidation-denitrification step and a short-cut sulfur autotrophic denitrification-anaerobic ammoxidation step;

the coagulating sedimentation step comprises the following steps: adding 1-5 mg/L of polyaluminum chloride (PAC), stirring at the rotating speed of 50-200 r/min for 20-30 min, then adding 0.8-1.2mg/L of Polyacrylamide (PAM), and stirring at the rotating speed of 90-110r/min for 20-30 min;

the anaerobic hydrolysis step comprises the following steps: setting the concentration of inoculated sludge to be 5000-12000 mg/L, the abundance of functional flora to be higher than 20%, and controlling the dissolved oxygen to be below 0.1 mg/L;

the synchronous nitrosation-anaerobic ammonia oxidation-denitrification step comprises the following steps: setting inoculated sludge containing anaerobic ammonium oxidation bacteria (Anammox), nitrosobacteria (AOB) and heterotrophic denitrifying bacteria, controlling the abundance of Anammox flora to be not less than 3%, the filling ratio of carrier filler to be 25-40%, and the specific surface area of filler to be 550-900 m ² /m ³ The concentration of mixed solution volatile suspended solids (MLVSS) is 3000-5000 mg/L, and the dissolved oxygen is controlled to be 0.1-05mg/L, the temperature is 30 to 37 ℃, and the free ammonia is controlled to be below 20 mg/L;

the short-range sulfur autotrophic denitrification-anaerobic ammonia oxidation (SSuDA for short) comprises the following steps: setting inoculated sludge containing Anamox bacteria and sulfur autotrophic denitrifying bacteria, taking sulfur as an electron donor, wherein the ratio of the sulfur to sodium carbonate is 0.4-0.6, the ammonia nitrogen of effluent water is 50-100 mg/L and the nitrate nitrogen is 150-250 mg/L according to the steps of synchronous nitrosation-anaerobic ammoxidation-denitrification, the sulfur adding concentration is 200-500mg/L, the filling ratio of a filling carrier is 20-30%, and the specific surface area of a filler is 650-750 m ² /m ³ The mixed solution MLVSS is 3000 to 5000mg/L, the temperature is 33 to 40 ℃, and the dissolved oxygen is controlled below 0.1 mg/L; final effluent quality ammonia Nitrogen (NH) ₄ ⁺ -N) concentration is controlled to be below 5mg/L, total nitrogen concentration TN is controlled to be below 10mg/L, and COD concentration is controlled to be 150-300 mg/L.

2. The method for efficiently denitrifying and decarbonizing the anaerobic effluent of the pig wastewater according to claim 1, which is characterized in that the total retention time of the four steps is 51 to 136h, the retention time of the coagulating sedimentation reaction is controlled to be 3 to 4h, the retention time of the anaerobic hydrolysis reaction is controlled to be 12 to 48h, the retention time of SNAD is controlled to be 24 to 48h, and the retention time of SSuDA is controlled to be 12 to 36h.

3. The method for efficiently denitrifying and decarbonizing the anaerobic effluent of the pig wastewater according to claim 1, wherein the coagulating sedimentation step is implemented in a coagulating sedimentation system, the coagulating sedimentation system comprises a coagulating stirring tank, a dosing tank a, a dosing tank b and a sedimentation tank a, PAM is contained in the dosing tank a, PAC is contained in the dosing tank b, the PAM and the PAC enter the coagulating stirring tank through a dosing pump a and a dosing pump b respectively, the effluent of the coagulating stirring tank enters the sedimentation tank a for mud-water separation, and sludge in a sludge bucket is removed every day.

4. The method for efficiently denitrifying and decarbonizing the anaerobic effluent of the pig wastewater according to claim 1, wherein the anaerobic hydrolysis step is implemented in an anaerobic hydrolysis system, the anaerobic hydrolysis system comprises a water inlet pump and an anaerobic hydrolysis reaction tank, the effluent of the sedimentation tank a is fed into the anaerobic hydrolysis reaction tank through the water inlet pump, and an air outlet and a sampling port are arranged at the top of the anaerobic hydrolysis reaction tank.

5. The method for efficiently denitrifying and decarbonizing the anaerobic effluent of the swine wastewater as claimed in claim 4, wherein the anaerobic hydrolysis reaction tank ensures a safe height between a mud layer and a water outlet by controlling the stirring speed, and a three-phase separator is arranged at the water outlet.

6. The method for efficiently denitrifying and decarbonizing the anaerobic effluent of the pig wastewater according to claim 1, wherein the synchronous nitrosation-anaerobic ammoxidation-denitrification step is implemented in a synchronous system, the synchronous system comprises an SNAD reaction tank, a flow meter, an aeration pump, a sedimentation tank b and a sludge reflux pump a, the effluent of the anaerobic hydrolysis reaction tank enters the SNAD reaction tank, the effluent of the SNAD reaction tank enters the sedimentation tank b for sludge-water separation, the sludge enters a sludge hopper and returns to the SNAD reaction tank through the sludge reflux pump a, and the lower part of the SNAD reaction tank is connected with the aeration pump through the flow meter.

7. The method for efficiently denitrifying and decarbonizing the anaerobic effluent of the swine wastewater according to claim 6, wherein the flow rate of the air pumped by the aeration pump is regulated by a flow meter so as to maintain the concentration of dissolved oxygen in the SNAD reaction tank, so that internal microorganisms are in a micro-aeration environment to ensure that most of total nitrogen is removed; the remaining ammonia nitrogen is used for maintaining the concentration of Free Ammonia (FA) in the SNAD reaction tank, so as to inhibit Nitrite Oxidizing Bacteria (NOB) without interfering main strains.

8. The method for efficiently denitrifying and decarbonizing the anaerobic effluent of the pig wastewater according to the claim 6, characterized in that the step of the short-range sulfur autotrophic denitrification-anaerobic ammonia oxidation is implemented in a short-range system, the short-range system comprises a reactor, a sedimentation tank c, a sludge reflux pump b and a dosing tank c, the effluent of the sedimentation tank b enters the reactor, the effluent of the reactor enters the sedimentation tank c for mud-water separation, and the sludge enters a sludge hopper and returns to the reactor through the sludge reflux pump b; the adding amount of the mixed liquid of sulfur and sodium carbonate in the adding pool c is adjusted through the adding pump c to control nitrate nitrogen to be reduced into nitrite nitrogen instead of being completely reduced into nitrogen, and then the mixed liquid and ammonia nitrogen in the effluent of the sedimentation pool b are subjected to anaerobic ammonia oxidation reaction, so that the purposes of deep denitrification and reduction of medicament consumption are achieved.

9. The method for efficiently denitrifying and decarbonizing the anaerobic effluent of the swine wastewater according to claim 8, wherein the mud scrapers are arranged in the sedimentation tank b and the sedimentation tank c, and the mud scrapers operate intermittently, and operate for 5 minutes every 6 hours, so that the effluent is clear while the sludge on the wall of the sedimentation tank is removed; the bottom slopes of the sedimentation tank b and the sedimentation tank c are set to be 50-70 degrees so as to ensure that as much sludge as possible slides into the mud bucket and flows back into the SNAD reaction tank and the reactor.

10. The method for efficiently denitrifying and decarbonizing the anaerobic effluent of the pig wastewater according to claim 8, wherein the mixed solution of sulfur and sodium carbonate, which is obtained by adding water and mixing in the dosing pool c, has a solid content of 10% -15%; adjusting according to the nitrate nitrogen concentration and the ammonia nitrogen concentration in the effluent of the SNAD reaction tank, and reducing all nitrate nitrogen into nitrite nitrogen and all ammonia nitrogen into nitrogen gas under the condition of ensuring that all ammonia nitrogen is reduced into nitrite nitrogen and all ammonia nitrogen is involved in the anaerobic ammonia oxidation reaction, wherein nitrite nitrogen which is not involved in the anaerobic ammonia oxidation reaction is reduced into nitrogen gas by the residual sulfur, so as to ensure the high-efficiency degradation of total nitrogen.

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